Catheter atherotome

ABSTRACT

A catheter atherotome and method for its use for performing partial atherectomy in an artery and thereby enlarging the lumen effectively available for blood flow through the artery. Several blades are mounted at a distal end of a catheter, in a helical basket configuration and spaced angularly apart from one another about the associated ends of two concentric sheaths in such a way that longitudinal and rotary relative movement of the sheaths selectively bows the blades arcuately outwardly into a cutting position or draws the blades flat into alignment with the sheaths. The blades have sharpened cutting edges extending helically and directed toward the catheter&#39;s proximal end when the blades are bowed. Partial removal of an atheroma is effected by manually pulling the basket knife past an atheroma with the basket blades in their outwardly bowed cutting positions, with the speed, force, and amount of expansion of the blades determined by the operator. Removal of cut-away pieces of atherosclerotic plaque material is accomplished either by pull-back of a balloon embolectomy catheter or by use of a latex membrane enshrouding the spiral wire blades to trap the shavings within the membrane.

This application is a continuation of application Ser. No. 07/395,500,filed Aug. 18, 1989, now abandoned.

BACKGROUND OF THE INVENTION

The present invention relates to surgical apparatus and procedures, andparticularly to a device for excising portions of the atheroscleroticplaque material causing stenosis in an artery.

Atherosclerosis (Greek for soft and hard deposits) is a condition whichprogressively affects many arteries of the body with advancing age. Itultimately produces thickening of the medial layer of the arterial wall,which may involve some or all of the circumference of the blood vessel.Eventually, narrowed internal diameter, or stenosis, of the arteryresults and restricts the flow of blood to the tissue beyond thestenosis, producing symptoms including angina or myocardial infarctionin the heart, claudication or gangrene in the legs, high blood pressure,or deterioration of kidney function.

The art and science involved in modern vascular surgery arecomparatively young and began with the successful end-to-end repair ofsevered arteries in Korean war casualties. Atherosclerotic narrowing ofarteries then could only be corrected by complete endarterectomy, whichrequired a longitudinal incision through the entire narrowed segment ofan artery. Exposure of an artery for this purpose was difficult, and thewounds resulting from the surgery were large. Although results wereoften gratifying, the practice was not widespread because of resultingproblems such as pseudoaneurysms developing in endarterized segments andthe potential for vessel wall dissection at the distal endpoint, andbecause of the difficulty posed both for the patient and for thesurgeon. During the 1950's a variety of synthetic tubular grafts wereintroduced and perfected for partial arterial replacement and bypassesaround stenoses. Because of the relative ease of such procedures bycomparison with endarterectomy, bypass grafting soon became the dominantmeans of correcting arterial narrowing within the pelvis and thigh.Advances in surgical technique in the late 1960's made possible the useof the patient's own reversed saphenous vein to bypass occluded arterieson the heart and below the knee.

As the population of the United States has aged as a group, themanifestations of atherosclerosis have, as a group, become this nation'snumber one health problem in terms of both suffering and cost. Whilesurgical bypass procedures using saphenous vein or prosthetic conduitremain the procedure of choice in most instances, newer technologieshave evolved in the last decade to simplify the treatment ofatherosclerotic stenoses in an attempt to reduce patient risk, reducecost, and to make treatment available to more people. In carefullyselected cases involving narrowing of short segments of the coronary,renal, iliac, and femoral arteries balloon dilation has been employedwith some success. Generally, however, the duration of arterial patencyresulting from such procedures is less than for bypass graft procedures.Utilization of lasers to open narrowed arteries has not yet proven to beclinically successful and is very expensive in all aspects.

In recent years a variety of atherectomy devices have been usedexperimentally in attempts to extend patency. Some of these devicesinclude rotary cutting mechanisms, which restrict their use to stenosesof short length. Some are driven by high-speed electric motors which addto their complexity and increase the likelihood of breakdown while alsoreducing the amount of responsiveness and taking the ability to controloperation out of the surgeon's hands.

Manually-operated devices for relieving arterial stenoses are disclosed,for example, in Lary U.S. Pat. No. 4,273,128, which discloses a devicehaving a plurality of curved knife blades whose edges are directedradially outward, and Fischell et al. U.S. Pat. No. 4,765,332, whichdiscloses a catheter including a proximally-exposed annular cutting edgewhich is no greater in diameter than an outer sleeve of the catheter towhich it is attached. Luther U.S. Pat. No. 4,650,466, discloses acatheter which includes an expansible woven tube portion which can beused to abrade atherosclerotic plaque from the interior wall of theartery. Clark, III, U.S. Pat. No. 4,020,847, discloses a catheter deviceincluding a slot having sharp edges extending longitudinally of thecatheter to cut free dangling matter which might otherwise obstruct thelumen of an artery. Hoffman U.S. Pat. Nos. 2,730,101 and 2,816,552disclose teat bistoury devices including blades which can be bowedoutwardly along the length of each blade to protrude radially. Thedevice is intended to be rotated to cut away restrictions in a milkcanal of a cow's teat. Several prior art devices useful for manuallyopening venous valves are disclosed in Chin et al. U.S. Pat. Nos.4,739,760 and 4,768,508 and Reed U.S. Pat. No. 4,655,217.

Chin U.S. Pat. No. 4,559,927 discloses an endarterectomy apparatusincluding a center-pull annular cutter for removing arterioscleroticmaterial.

Rotary, mechanically operated devices are disclosed in such patents asSokolik U.S. Pat. No. 3,320,957, which discloses a device including anarray of helical stationary blades inside which an oppositely-twistedhelical rotor operates to shear material protruding inwardly between thestationary blades. Auth U.S. Pat. No. 4,445,509 discloses a flutedrotary burr. Kensey U.S. Pat. Nos. 4,589,412 and 4,631,052 discloseturbine-driven rotary devices for opening obstructed arteries, andKensey et al. U.S. Pat. No. 4,681,106 discloses another turbine-drivenrotary cutting device.

Several devices for use in retrieving stones from within bodilypassageways by entrapping the stones within baskets including arrays ofhelical wires are disclosed in Grayhack et al. U.S. Pat. No. 4,611,594,Duthoy U.S. Pat. No. 4,625,726, Dormia U.S. Pat. Nos. 4,347,846 and4,612,931. Related devices are disclosed by McGirr U.S. Pat. No.4,807,626, and Hawkins, Jr. et al. U.S. Pat. No. 4,790,812, whichdiscloses a parachute-like basket carried on a distal end of a rotatableinterior member of a catheter so that the parachute-like basket canretrieve particles cut free by the interior member of the catheter. ParkU.S. Pat. No. 3,704,711 discloses a device in which a radially outwardlydisposed edge can be controllably concealed within a distal end of acatheter or exposed so that the blade can be used.

Balloon-tipped catheters are disclosed in Fogarty U.S. Pat. No.3,435,826, while Fogarty U.S. Pat. No. 3,472,230 discloses a catheterincluding an umbrella-like skirt useful for retrieval of stones.

There still remains a need, however, for an improved atherectomy devicewhich is simple in concept and operation, manually operable, andimmediately responsive, and which is useful for all stenoses regardlessof the length of the area of stenosis.

SUMMARY OF THE INVENTION

The present invention overcomes some of the shortcomings anddisadvantages of the devices disclosed in the prior art by providing acatheter atherotome which is manually operable and by which a surgeoncan plane away atherosclerotic plaque from within an artery by enteringthe artery with a catheter at a single point proximal to the plaquedeposit. The plaque is cut away piecemeal, by serial pullback strokes ofa basket knife carried on the distal end of the catheter and which iscollapsible to a small diameter conforming to the diameter of thecatheter itself. The basket knife of the catheter atherotome includesseveral blades which are aligned generally parallel with one another andin a generally helical arrangement about an inner portion of thecatheter which extends distally beyond the distal end of an outer sheathportion of the catheter when in a retracted, relaxed configuration.Respective ends of each blade are attached to the inner member and theouter sheath of the catheter so that when the distal end of the innermember is moved closer to the distal end of the outer sheath the blademembers are forced to bow outward, expanding the basket knife radially.When the blades are bowed outward, sharpened edges of the blades areexposed proximally with respect to the catheter, so that moving thecatheter proximally brings the edges to bear against atheroscleroticplaque deposits to cut them away from the interior of an artery.

While it is particularly well-adapted for use in the femoral andpopliteal arteries, the catheter atherotome of the invention may also beuseful in the tibial and peroneal arteries, and with entry gained viathe aorta, in the heart and renal arteries.

In a preferred embodiment of the invention, both the longitudinalposition and the rotational position of the inner member of the catheterare adjustable relative to the outer sheath, and the several blades areflexible, so that both the pitch and the amount of radial bowing of theblades are controllable Preferably, the angle of attack of the sharpenededge is such that it will engage atherosclerotic plaque but not normalarterial lining tissue.

Another embodiment of the invention utilizes a more rigid basket knifein which sharpened portions of the blades overlap one another to providecomplete circumferential coverage of the interior of an artery.

Yet another embodiment of the basket knife portion of the deviceincludes cutting edges over only about half of the basket circumference,so that atherectomy can be performed on one-half of the arterial wall inlocations where atherosclerosis normally involves only the posteriorone-half of the artery.

Preferably, a lumen is provided in the inner member of the catheter, anda balloon-tipped catheter such as a Fogarty® catheter is utilized tocollect shavings of plaque cut free by the catheter atherotome of theinvention, so that the shavings can be surgically removed through anincision in the arterial wall after atherectomy has been performed.

In another embodiment of the invention a latex skirt is provided tosurround the basket knife assembly except where the cutting edges areprovided, so that the shavings are trapped within the basket during eachcutting pass of the basket knife over the plaque. This embodiment isintended for use in smaller arteries where it might be awkward orimpractical to insert a balloon-tipped catheter, or where the catheteratherotome is introduced into an artery percutaneously.

In percutaneous use of the catheter atherotome of the invention a needleis inserted through the skin into an artery. A guide wire is passedthrough the needle bore and directed to the point of stenosis in thearterial system. The needle is removed and a dilator is passed over theguide wire and then removed, after which the catheter atherotome isinserted into the artery following the guide wire through the dilatedtract into the artery and on to the point of stenosis. After appropriateexcision of atherosclerotic plaque, the catheter atherotome and guidewire are removed and pressure is held at the point of skin puncture topermit closure of the artery to occur.

Objective confirmation of enlargement of the arterial lumen by the useof the catheter atherotome could be obtained either by on-the-tableangiography, for comparison with the pre-operative arteriogram, or anon-the-table duplex-ultrasound measurement could be made of the arteriallumen immediately before and after use of the catheter atherotome of thepresent invention.

It is, therefore an important object of the present invention to providean improved catheter atherotome for use in relief of stenoses inarteries

It is another important object of the present invention to provide sucha device which is manually adjustable between a configuration in whichcutting blades are retracted and a configuration in which cutting bladesare operatively positioned and exposed to a degree controllable by theuser of the device.

It is an important feature of the apparatus of one embodiment of thepresent invention that its blades are somewhat flexible, between aposition in which they move along the interior of healthy portions of anartery, and a position in which they cut away atherosclerotic plaque.

The foregoing and other objectives, features, and advantages of theinvention will be more readily understood upon consideration of thefollowing detailed description of the invention, taken in conjunctionwith the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a pictorial view of a catheter atherotome which embodies thepresent invention, with the catheter portion shown foreshortened, andwith the basket knife in a retracted or closed position.

FIG. 2 is a sectional view of the catheter atherotome shown in FIG. 1,taken along the line 2--2 of FIG. 1, and simplified by omission of someof the blades of the basket knife.

FIG. 3 is a view similar to FIG. 2, with the basket knife in anexpanded, or cutting configuration.

FIG. 4 is an edge-on view of one of the blades of the basket knife ofthe atherotome shown in FIGS. 1-3.

FIG. 5 is a side view of the blade shown in FIG. 4.

FIG. 6 is a sectional view, taken along line 6--6 of the blade shown inFIGS. 4 and 5.

FIG. 7a is a perspective view, taken in the direction indicatedgenerally by line 7a--7a of FIG. 1, showing a fitting for attaching thedistal end of each blade to the end of the inner member of the catheteratherotome shown in FIGS. 1-3.

FIG. 7b is a perspective view, taken in the direction indicatedgenerally by the line 7b--7b in FIG. 1, of the fitting attaching theproximal ends of the blades to the distal end of the outer sheathportion of the catheter atherotome shown in FIGS. 1-3.

FIG. 8 is a schematic view showing the arrangement of the several bladesof one embodiment of the catheter atherotome of the present invention.

FIG. 9 is a view similar to that of FIG. 8, of a set of somewhatdifferent blades for the basket knife of the catheter atherotome ofFIGS. 1-3.

FIG. 10 is a view similar to that of FIG. 8, schematically showing athird set of blades which embody the invention.

FIG. 11a is a pictorial view of the basket knife portion of a catheteratherotome of an alternate embodiment of the invention, including askirt portion associated with the blades of the basket knife.

FIG. 11b is a fragmentary side elevation view showing a detail of theembodiment of the invention shown in FIG. 11.

FIGS. 12a, 12b, and 12c are sectional views of a portion of an arteryincluding an atheroma, showing the action of the catheter atherotome ofthe present invention as it is drawn past the atheroma to remove aportion of the plaque material forming the atheroma.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings which form a part of the disclosureherein, in FIGS. 1-3 a catheter atherotome 10 includes an elongateflexible tubular outer sheath 12. A similar inner member 14 of somewhatgreater length is disposed within the of the outer sheath 12. The outersheath 12 and inner member 14 are flexible enough to negotiate curves inarteries atraumatically, but are rigid enough to maintain relativeposition between the two, both longitudinally and rotationally. Theymight be made, for example, of a suitable polyvinyl chloride plasticmaterial. Markings 15 may be provided along the outer sheath 12 toindicate the length of the catheter atherotome distal of each marking asan aid to placement in an artery.

A first lever 16 is connected with the outer sheath 12 near its proximalend. A second lever 18 is pivotally connected with the first lever 16 ata pivot joint 19. An elongate loop 20 is attached to the second lever 18and surrounds the rear or proximal end portion 21 of the inner member14. A stop 22 is fixedly attached to the proximal end of the innermember 14. The stop 22 is preferably larger than the loop 20 and isprovided with appropriate surface configuration to permit rotation ofthe inner member 14 manually with respect to the outer sheath 12 by useof the stop 22. Finger loops are provided on the levers 16 and 18 foruse in manipulation of the first and second levers 16 and 18 to withdrawthe proximal end 21 of the inner member 14 a distance from the proximalend 23 of the outer sheath 12, as desired. A second stop 25 ispreferably also located on the inner member 14, on the distal side ofthe loop 20, to be used, if necessary, to push the inner member 14distally into the proximal end 23 of the outer sheath 12. Preferably, ascale 24 is provided on the first lever 16 as an indicator of theposition to which the inner member 14 has been withdrawn relative to theouter sheath 12. A cap 26 is mounted on the proximal, or rear end of theouter sheath 12 by means of mating threads, and an O-ring 28, held inplace by the cap 26, grips the exterior surface of the inner member 14with an appropriately adjustable amount of force to maintain theposition of the inner member 14 relative to the outer sheath 12.

The inner member 14 is tubular, with a lumen which is large enough toadmit passage of a guide wire (not shown) or a balloon-tipped catheter30 which may, for example, be a Fogarty® arterial embolectomy catheter.

A controllably expansible basket knife 32 includes a plurality of blades34 extending between the distal end 35 of the outer sheath 12 and thedistal end 37 of the inner member 14, which extends, as previouslymentioned, beyond the distal end of the outer sheath 12. While sixblades, equally spaced, are shown, fewer or more might also be utilized.The catheter atherotome 10 can be of an appropriate size, depending onthe size of the artery, and larger blades 34 are required for largerarteries.

As shown in FIGS. 1 and 2, when the inner member 14 is located with itsdistal end 37 in a position of maximum extension beyond the distal end35 of the outer sheath 12, the blades 34 extend closely alongside theprotruding portion of the inner member 14, normally in a helicalconfiguration centered about a central longitudinal axis 36. The distalends 38 of the several blades 34 are separated from the positions of theproximal ends 40 of the blades 34, by an angle determined by therotational position of the inner member 14 with respect to the outersheath 12. Thus, rotation of the inner member 14 within the outer sheath12 causes a steeper or shallower slope or pitch of each of the blades34. Thus, as shown in FIG. 1, the distal ends 38 of the blades arelocated approximately 60° offset from the respective proximal ends 40,with the blades 34 extending generally longitudinally and closelyalongside the inner member 14, in a steep helix.

It should be recognized that FIGS. 2 and 3, for the sake of clarity,show but two of the blades 34, of which there would normally be agreater number, for example, six blades 34. It should further berecognized that the inner member 14 is shown in a position of rotationrelative to the position of the outer sheath 12 in which the distal ends38 are separated from the respective proximal ends 40 by about 180° .This exaggerates the degree of rotation which probably would be used inpractice, in order to provide greater clarity in the figures fordepiction of the effects of a combination of rotation and retraction ofthe inner member 14 with respect to the position of the outer sheath 12.

Referring now also to FIGS. 4, 5, and 6, it will be seen that each blade34 includes a middle portion 42 including a sharpened edge 44, anintermediate, or strut, section 46, between the distal end 38 and themiddle portion 42, and an intermediate, or strut, portion 48, locatedbetween the middle portion 42 and the proximal end 40. A pair of fins, afin 50 proximate the distal end 38 and a parallel fin 52 proximate theproximal end 40 of the blade, respectively define bores 54 and 56. Thefins 50 and 52 are oriented generally perpendicular to the orientationof a plane defined by the middle portion 42 of the blade, and the bores54 and 56 extend generally normal to the fins 50 and 52, while theblades 34 are gently curved in an "S" shape when relaxed.

The catheter 30 extending through the catheter atherotome 10 has aballoon tip 60 which extends beyond the distal end of the catheteratherotome 10, as may be seen in FIG. 1. The catheter 30 is longer thanthe entire catheter atherotome 10, so that it can be manipulated at theproximal end of the catheter atherotome 10 while extending through alumen 62 defined within the inner member 14, as shown in FIGS. 2 and 3.Such length is also desirable to provide room for cutting strokes of theatherotome with the balloon tipped catheter stationary in an artery.

The intermediate, or strut, portions 46 and 48 of each blade 34 areflexible in response to movement of the inner member 14 relative to theouter sheath 12, so that rotation of the inner member and retraction ofthe distal end 37 of the inner member with respect to the distal end 35of the outer sheath result in flexure of the blades 34. Flexure takesplace particularly in the strut portions 48 and 46 of the blades 34, toexpand the plurality of blades 34 into a basket-like configuration inwhich each edge 44 is inclined more steeply with respect to the centrallongitudinal axis 36. While the strut portions 48 and 46 are free tobend relatively uniformly and to twist, the wider and more flattenedshape of the sharpened middle portion 42 constrains its flexure to adegree which permits the edge 44 to assume an arcuate curvature centeredabout the inner member 14 but at a radius greater than that of the outersheath 12, with the sharpened edge 44 directed toward the proximal endof the catheter atherotome 10. The inclination of the individual blades34, and particularly the edge 44 thereof, is determined by both thedegree to which the inner member 14 is withdrawn proximally within thedistal end 35 of the outer sheath 12, and the degree of rotation of theinner member 14 with respect to the outer sheath 12. Preferably, theedge 44 can extend up to an angle of 40° to 50° relative to an imaginaryequator of the basket knife 32 to achieve maximum cutting, with theequator considered to be normal to the longitudinal axis 36.

As may be seen with reference more particularly to FIGS. 7a and 7b, aswell as FIGS. 2 and 3, the blades 34 are prevented from rotating withrespect to the inner member 14 and outer sheath 12 by the manner inwhich they are attached. An articulating mounting ring 64 extendsthrough the bores 54 of all of the several blades 34. The articulatingmounting ring 64 is securely attached to a distal fitting 66, which hasan ogival shape. The fitting 66 is attached to the distal end 37 of theinner member 14 by exterior threads defined on the inner member 14 andinterior threads in the distal fitting 66. A bore 68 in the distalfitting 66 is an extension of the lumen 62 of the inner member 14.

The articulating mounting ring 64 is attached to the proxmal end of thedistal fitting 66 by a plurality of tethering hasps 70 disposed aboutthe proximal end of the distal fitting 66 and equal in number to thenumber of blades 34 to be attached to the distal fitting 66. Each of thetethering hasps 70 is bent inwardly to form an arch over thearticulating mounting ring. Adjacent ones of the several tethering hasps70 cooperatively define radially extending slots 72 between one another,with the fin 50 of a respective one of the blades 34 being disposedwithin each of the slots 72. The slots 72 and fins 50 restrain each ofthe blades 34 from rotation about an axis parallel with the centrallongitudinal axis 36, but permit a terminal portion of each blade,including the fin 50 and the strut or intermediate portion 46, to pivot,about the articulating mounting ring 64 as the blade 34 is bowed.

A proximal blade fitting 76 is attached to the distal end 35 of theouter sheath 12 by exterior threads mated with interior threads definedin the outer sheath 12. An articulating mounting ring 78, similar to thearticulating mounting ring 64, extends through the several bores 56defined by the fins 52 of the blades 34, interconnecting all of theproximal ends 40 of the blades. The articulating mounting ring 78 isattached to the proximal fitting 76 by a plurality of tethering hasps 80equal in number to the number of blades 34.

Similar to the tethering hasps 70, the tethering hasps 80 extend fromthe distal face of the proximal fitting 76 and are bent arcuately inwardtoward the central longitudinal axis 36 of the catheter atherotome 10,arching over and retaining the articulating mounting ring 78. Thetethering hasps 80 define radially extending slots 82 between adjacentones of the hasps 80 and restrict the proximal ends 40 of the severalblades 34 from rotating about an axis parallel with the centrallongitudinal axis 36 of the catheter atherotome 10. Terminal portions ofthe blades 34 located adjacent the proximal ends 40 are free to pivotwith the fins 52 rotating about the articulating mounting ring 78 inresponse to retraction of the distal end of the inner member 14 into thedistal end of the outer sheath 12 to the position shown, for example, inFIG. 3.

Referring to FIGS. 8, 9, and 10, the configuration and degree offlexibility of a set of blades 34 may be made to provide differentamounts of coverage of the circumference of the interior or lumen of anartery within which partial arterotomy is to be performed.

In FIG. 8, six blades 34a for use as part of the catheter atherotome 10according to the present invention are shown in a simplified schematicform as if the articulating mounting rings 64 and 78 had beenstraightened and unwrapped from around the circumference of the innermember 14, while maintaining the circumferential spacing of the blades34a so as to show the angular relationships between their respectiveopposite ends. It will be seen, then, that the angular distance of thedistal ends 38a from the proximal ends 40a is greater than 60° . Thus,the distal end of one of the blades 34a is offset angularly beyond theproximal end 40 of the adjacent blade 34a, and the middle portions 42aof adjacent blades 34a also overlap one another so that the edges 44acooperatively present a substantially continuous circular combination ofcutting edges 44a to remove a layer of plaque from the entire interiorsurface of the atheroma being reduced on each cutting stroke of theatherotome. The blades 34a preferably are stiff enough so that the angleof incidence of the cutting edge is fairly stable, so that the cuttingedge can pare off a thin slice of atherosclerotic plaque or similarmaterial from the interior of an artery during use of the catheteratherotome 10 equipped with the blades 34a.

Referring now more particularly to FIG. 9, a set of blades 34b are shownwhich have less offset between the locations of their distal ends 38band their proximal ends 40b, so that the cutting edges 44b make separatecuts which do not overlap one another ordinarily. However, the blades34b are made with greater flexibility and less torsional rigidity thanthe blades 34a. This is so that, although the angle of incidence of theedges 44 ordinarily is too little to result in cutting the interior ofthe arterial wall, when the sharp edge 44b of an individual blade 34b"snags" on a hard irregular body of plaque the blade is everted into acutting position with a somewhat greater angle of incidence in order toexcise that piece of plaque, as will be explained more fullysubsequently. Because of the lesser offset between the distal andproximal ends of the blades 34b there is an interrupted coverage of thecircumference of an artery, providing space for irregular protrusions ofplaque to project between the blades 34b to be engaged by the sharpenededges 44b.

In FIG. 10 is shown a set of blades 34c and 34d, of which only the threeblades 34c include middle portions 42c having edges 44c, while theblades 34d have no sharpened edge portions. Thus, the set of blades 34cand 34d provide cutting edge coverage over only about one-half theinterior circumference of an artery and are most useful in removingplaque from the posterior side of an artery such as the femoral artery,where atheroma normally occurs only on the posterior side of the artery.The wire blades 34d without edges then help to maintain the properrelationship between the blades 34c, and keep the basket knife apparatuscentered within the arterial lumen.

In some instances a catheter atherotome may be required to be of a sizethat is too small to admit passage of the balloon-tipped catheter 30therethrough. It is still necessary to be able to retrieve pieces ofplaque which have been cut free from the interior wall of an artery byuse of the atherotome. In order to recover the matter excised from anarterial wall, a catheter atherotome 90, shown in FIGS. 11a and 11b,which is otherwise similar to the catheter atherotome 10, additionallyincludes a flexible tubular membrane in the form of a skirt 92 arrangedabout and attached to the blades 34. One end of the skirt is attached tothe distal fitting 66 by means of ferrules 91 and the other end isattached to the proximal fitting 76 by means of ferrules 93. The skirt92 is preferably adherently attached to the blades 34, at least alongthe middle portions 42, and slits 94 or equivalent openings are providedto expose the edges 44 and provide ingress for pieces of plaque to theinterior of the skirt 92. Pieces of plaque or the like cut free from theinterior wall of an artery are able to pass through the slits 94 to becollected upon retrieval of the catheter atherotome 90 from within anartery. The membrane used as the skirt 92 must be flexible and thin, yetstrong and elastic enough to accommodate the adjustment of the basketknife 32. A suitable material is a thin sheet latex. The skirt 92 may beattached to distal fitting 66 and the proximal fitting 76 after assemblyof the catheter atherotome 10 including the blades 34.

Referring now to FIGS. 12a, 12b, and 12c, showing a portion of an artery96 including an atheroma 98, the catheter atherotome 10 is illustratedschematically to show its use. As shown in FIG. 12a, the catheteratherotome 10 has been inserted into the artery from right to left.Thereafter, the inner member 14 has been withdrawn a distance into thedistal end 35 of the outer sheath 12, so that the blades 34 are bowed,to place the middle portion 42 of each blade at an increased radialdistance away from the inner member 14 and to cause the sharpened edges44 to come into proper position.

To excise a portion of the atheroma 98, the catheter atherotome ismanually pulled to the right as shown in FIG. 12b, and as indicated bythe arrow 100. As the inwardly projecting atheroma 98 is encountered bythe upper blade 34, and particularly by the edge 44, engagement of theedge 44 in the atheroma plaque material causes the edge 44 to be evertedinto a cutting position in which it digs into the plaque material andbegins to cut a portion of the plaque material free, as may be seen inFIG. 12c. Torsional forces developed in the strut portions 46 and 48control the angle of incidence of the edge 44, allowing the middleportion 42 to be moved to such a cutting position when plaque isencountered. However, where there is no plaque material present, as inthe lower portions of the artery shown in FIGS. 12a, 12b, and 12c, theedge 44 of the respective blade 34 is oriented so that it does not catchthe intima of the arterial wall and simply slides along the interiorwall of the artery without doing any cutting.

The surgeon using the catheter atherotome 10 can repeatedly move thebasket knife 32 back and forth in the area of an atheroma such as theatheroma 98, cutting away a thin layer of plaque with each pass in thedirection indicated by the arrow 100 in FIGS. 12b and 12c, until thelumen of the artery 96 has been opened sufficiently. After each cuttingstroke the entire catheter atherotome 10 will be rotated through anangle which can be determined by the position of the levers 16 and 18,so as to result in excision of plaque in an evenly distributed patternabout the interior of the artery. Thereafter, the inner member 14 may beallowed to resume its extended position beyond the distal end of theouter sheath 12, using the loop 20 (see FIG. 1) against the second stop25 if necessary, thus retracting the middle sections 42 of the blades 34closer to the inner member 14. The catheter atherotome 10 can then bewithdrawn from the artery, followed by withdrawal of the balloon-tippedcatheter 30, with the balloon 60 (see FIG. 1) inflated to retrieve thematerial which has been cut free from the arterial wall during theprocess.

The procedure is similar when using the catheter atherotome 90 (FIG.11a), except that the material cut free from the arterial wall would beretained within the membrane skirt 92 for retrieval along with theatherotome 90 when it is withdrawn from the artery.

The catheter atherotome 10 may be introduced into an artery including astenosis by providing access to the artery and opening the arterial wallat a position more proximal to the heart than the location of thestenosis. Preferably, a guide wire is introduced into the artery andpast the stenosis. Thereafter, if required, a dilator may be introducedinto the artery, guided by the wire. The dilator may then be withdrawnand the catheter atherotome 10 according to the present invention may beinserted into the artery along the guide wire, which may then bewithdrawn and replaced by the balloon-tipped catheter 30. Afterinflation of the balloon 60 to prevent loss of pieces of material cutfree from the arterial wall by the atherotome 10, the basket knife 32may be expanded to the required size by withdrawal of the inner member14 into the distal end 35 of the outer member 12 a required distance bysqueezing together the finger loops of the levers 16 and 18, so that theelongate loop 20 acts upon the stop 22 to withdraw the proximal end 21of the inner member 14 at the proximal end of the catheter atherotome10. Preferably, the scale 24 provided on the lever arm 16 may be used todetermine when the inner member 14 has been withdrawn sufficiently toprovide the required expansion of the basket knife 32.

Thereupon, the catheter atherotome may be withdrawn past the location ofthe atheroma, with the sharpened edges 44 of the blades 34 of the basketknife 32 paring away a portion of the plaque from the interior of theartery. The atherotome is then pushed into the artery until the blades34 are beyond the atheroma, and rotated to a desired position for asubsequent pull-back cutting stroke. After several strokes, for example,six to ten cutting strokes, sufficient enlargement of the lumen of theartery should have taken place, and the basket blade 32 can be relaxed,contracting the blades 34 into position alongside the inner member 14 asshown in FIG. 1, so that the atherotome can be withdrawn from theartery.

The terms and expressions which have been employed in the foregoingspecification are used therein as terms of description and not oflimitation, and there is no intention in the use of such terms andexpressions of excluding equivalents of the features shown and describedor portions thereof, it being recognized that the scope of the inventionis defined and limited only by the claims which follow.

What is claimed is:
 1. A catheter atherotome for use in surgical removalof plaque from the interior wall of an artery, comprising:(a) anelongate tubular outer sheath having respective proximal and distalends; (b) an elongate inner member disposed within said outer sheath andhaving respective proximal and distal ends, said distal end of saidinner member extending beyond said distal end of said outer sheath; (c)a plurality of elongate blades each having a proximal end interconnectedwith said outer sheath and a distal end interconnected with said innermember; (d) means for moving said inner member with respect to saidouter sheath so as to retract said distal end of said inner membertoward said distal end of said outer sheath and flex said blades into aradially outwardly bowed arcuate configuration; and (e) at least some ofsaid blades defining respective sharp edges, at least a portion of eachsaid sharp edge extending alongside said inner member and facinggenerally more toward said proximal ends than toward said distal ends ofsaid outer sheath and said inner member, the ones of said bladesarranged over approximately one-half the circumference of said outersheath and inner member including said sharp edges while the remainderof said blades are free from said sharp edges.
 2. A catheter atherotomefor use in surgical removal of plaque from the interior wall of anartery, comprising:(a) an elongate tubular outer sheath havingrespective proximal and distal ends; (b) an elongate tubular innermember disposed within said outer sheath and having respective proximaland distal ends, said distal end of said inner member extending beyondsaid distal end of said outer sheath; (c) a plurality of elongate bladeseach having a proximal end interconnected with said outer sheath and adistal end interconnected with said inner member; (d) means for movingsaid inner member with respect to said outer sheath so as to retractsaid distal end of said inner member toward said distal end of saidouter sheath and flex said blades into a radially outwardly bowedarcuate configuration; and (e) at least some of said blades definingrespective knife-like sharpened edges, at least a portion of each saidknife-like sharpened edge extending alongside said inner member andbeing oriented more toward said proximal ends than toward said distalends of said outer sheath and said inner member when said blades are insaid outwardly bowed arcuate configuration, so as to engage plaqueassociated with an inner wall of an artery cuttingly as said catheteratherotome is moved within said artery in a proximal direction, withoutengaging said interior wall of said artery cuttingly as said catheteratherotome is moved within said artery in a distal direction, each ofsaid blades defining a knife-like sharpened edge including a middleportion defining said knife-like sharpened edge and a pair ofintermediate portions adjacent said middle portion, said intermediateportions being sufficiently more flexible than said middle portion thatsaid middle portion substantially retains its original shape duringflexing of said blades into said radially outwardly bowed arcuateconfiguration.
 3. The catheter atherotome of claim 2 wherein said innermember defines lumen means for receiving a guide wire extending throughsaid inner member for guiding said catheter atherotome within saidartery.
 4. The catheter atherotome of claim 2 wherein said means formoving said inner member includes lever-operated means for moving saidinner member longitudinally with respect to said outer sheath and meansassociated with said inner member for rotating said inner member withrespect to said outer sheath.
 5. The catheter atherotome of claim 2wherein each of said elongate blades includes flexible portions thereofwhich do not define an edge thereof.
 6. The catheter atherotome of claim2 wherein said inner member defines a central longitudinal axis, andincluding means for preventing at least one of said ends of each of saidblades from rotating with respect to said outer sheath and said innermember about an axis extending generally parallel with said centrallongitudinal axis, while permitting a terminal portion of each of saidblades to rotate about an axis extending substantially perpendicular tosaid central longitudinal axis, between a position in which saidterminal portion extends generally parallel with said longitudinal axisand a position in which said terminal portion extends away from saidlongitudinal axis at an acute angle and said middle portion of saidblade is displaced radially away from said longitudinal axis.
 7. Thecatheter atherotome of claim 6 wherein at least one said terminalportion of each of said blades includes fin means for defining a bore,said bore defining an axis of rotation of said at least one terminalportion relative to a respective one of said inner member and said outersheath to which said at least one end is attached.
 8. The catheteratherotome of claim 2 wherein each of said knife-like sharpened edges ofsaid blades is located in a cutting position exposed toward saidproximal end of said outer sheath and extending generallycircumferentially about said inner member when said distal end of saidinner member is retracted toward said distal end of said outer sheathand said blades are in said outwardly bowed arcuate configuration. 9.The catheter atherotome of claim 2 wherein said inner member is tubular,further including balloon-tipped catheter means, disposed within andextending through said inner member and having an inflatable balloon tiplocated distally beyond said distal end of said inner member and blades,for retaining and retrieving pieces of material cut free from anatheroma during use of said catheter atherotome.
 10. The catheteratherotome of claim 2 further including skirt means of flexiblemembranous material, arranged about said blades for retrieving pieces ofmaterial from within an artery.
 11. The catheter atherotome of claim 2,said plurality of blades defining a basket when said distal end of saidinner member is retracted toward said distal end of said outer sheath,said basket defining an equator, and said respective knife-lifesharpened edges of said blades being located along said equator portionof said basket.
 12. The catheter atherotome of claim 2 said intermediateportions being resiliently flexible and twistable, and each saidknife-like sharpened edge normally being oriented helically about acentral longitudinal axis of said inner member and defining an angle ofattack, said angle of attack being shallow enough so that saidknife-like sharpened edge ordinarily will not cuttingly engage thesurface of the interior tissue of a healthy artery but great enough sothat said knife-like sharpened edge will cuttingly engageatherosclerotic plaque projecting from the interior surfaces of anartery, said intermediate portions being torsionally elastic enough topermit said middle portions of said blades to rotate resiliently to aposition in which said knife-like sharpened edges can engage and pareaway a portion of said plaque material from said interior surfaces ofsaid artery.
 13. A catheter atherotome for use in surgical removal ofplaque from the interior wall of an artery, comprising:(a) an elongatetubular outer sheath having respective proximal and distal ends; (b) anelongate inner member disposed within said outer sheath, said innermember having respective proximal and distal ends and defining a centrallongitudinal axis and said distal end of said inner member extendingbeyond said distal end of said outer sheath; (c) a plurality of elongateblades each having a proximal end interconnected with said outer sheathand a distal end interconnected with said inner member; (d) means formoving said inner member with respect to said outer sheath so as toretract said distal end of said inner member toward said distal end ofsaid outer sheath and flex said blades into a radially outwardly bowedarcuate configuration; (e) at least some of said blades definingrespective sharp edges, at least a portion of each said sharp edgeextending alongside said inner member and facing generally more towardsaid proximal ends than toward said distal ends of said outer sheath andsaid inner member; (f) means for preventing at least one of said ends ofeach of said blades from rotating with respect to said outer sheath andsaid inner member about an axis extending generally parallel with saidcentral longitudinal axis, while permitting a terminal portion of eachof said blades to rotate about an axis extending substantiallyperpendicular to said central longitudinal axis, between a position inwhich said terminal portion extends generally parallel with saidlongitudinal axis and a position in which said terminal portion extendsaway from said longitudinal axis at an acute angle and said middleportion of said blade is displaced radially away from said longitudinalaxis; (g) fin means included in at least one of said terminal portionsof each of said blades, for defining a bore, each said bore defining anaxis of rotation of a respective one of said terminal portions relativeto a respective one of said inner member and said outer sheath to whichsaid respective one of said terminal portions is attached; and (h)mounting means for attachment of said blades to said inner member andsaid outer sheath, said mounting means defining radial slot means forcooperating with said fin means of each of said blades, so assubstantially to prevent said terminal portions of each of said bladesfrom rotating about an axis parallel with said central longitudinal axisof said inner member.
 14. The catheter atherotome of claim 13 whereinsaid mounting means includes a distal fitting fixedly attached to saidinner member, a distal end of each of said blades being movably attachedto said distal fitting.
 15. A catheter atherotome for use in surgicalremoval of plaque from the interior wall of an artery, comprising:(a) anelongate flexible tubular outer sheath having respective proximal anddistal ends; (b) an elongate flexible tubular inner member disposedwithin said outer sheath and having respective proximal and distal ends,said distal end of said inner member extending beyond said distal end ofsaid outer sheath; (c) a plurality of elongate knife blades each havinga proximal end interconnected with said outer sheath and a distal endinterconnected with said inner member; (d) at least some of said knifeblades defining respective knife-like sharp edges, at least a portion ofeach said knife-like sharp edge extending alongside said inner memberand facing more toward said proximal ends than toward said distal endsof said outer sheath and said inner member, said knife blades defining adiameter of said catheter atherotome and each knife blade having a pitchwith respect to said inner member; (e) means for moving said innermember with respect to said outer sheath so as to retract said distalend of said inner member toward said distal end of said outer sheath andflex said knife blades into a radially outwardly bowed arcuateconfiguration of increased diameter; and (f) means for rotating saidinner member with respect to said outer sheath so as to control thepitch of said knife blades.
 16. A catheter atherotome for use insurgical removal of plaque from the interior wall of an artery,comprising:(a) an elongate flexible tubular outer sheath havingrespective proximal and distal ends; (b) an elongate flexible tubularinner member disposed within said outer sheath and having respectiveproximal and distal ends, said distal end of said inner member extendingbeyond said distal end of said outer sheath; (c) a plurality of elongateknife blades each having a proximal end interconnected with said outersheath and a distal end interconnected with said inner member; (d) atleast some of said knife blades defining respective knife-like sharpedges, at least a portion of each said knife-like sharp edge extendingalongside said inner member and facing more toward said proximal endsthan toward said distal ends of said outer sheath and said inner member,said knife blades defining a diameter of said catheter atherotome andeach knife blade having a pitch with respect to said inner member; (e)means for moving said inner member with respect to said outer sheath soas to retract said distal end of said inner member toward said distalend of said outer sheath and flex said knife blades into a radiallyoutwardly bowed arcuate configuration of increased diameter; and (f)means for controlling said pitch and said diameter while using saidcatheter atherotome.
 17. A catheter atherotome for use in surgicalremoval of plaque from the interior wall of an artery, comprising:(a) anelongate tubular outer sheath having respective proximal and distalends; (b) an elongate inner member disposed within said outer sheath andhaving respective proximal and distal ends, said distal end of saidinner member extending beyond said distal end of said outer sheath; (c)a plurality of elongate blades each having a proximal end interconnectedwith said outer sheath and a distal end interconnected with said innermember; (d) means for moving said inner member with respect to saidouter sheath so as to retract said distal end of said inner membertoward said distal end of said outer sheath and flex said blades into aradially outwardly bowed arcuate configuration; and (e) at least some ofsaid blades defining respective sharp edges, at least a portion of eachsaid sharp edge extending alongside said inner member and being orientedmore toward said proximal ends than toward said distal ends of saidouter sheath and said inner member when said blades are in saidoutwardly bowed arcuate configuration, so as to engage plaque associatedwith an inner wall of an artery cuttingly as said catheter atherotome ismoved within said artery in a proximal direction, without engaging saidinterior wall of said artery cuttingly as said catheter atherotome ismoved within said artery in a distal direction and at least one of saidsharp edges having respective opposite first and second ends, said firstand second ends thereof being angularly separated from each other by acontrollably variable angle about said inner member when said blades arein said outwardly bowed arcuate configuration.
 18. A catheter atherotomefor use in surgical removal of plaque from the interior wall of anartery, comprising:(a) an elongate tubular outer sheath havingrespective proximal and distal ends; (b) an elongate inner memberdisposed within said outer sheath and having respective proximal anddistal ends, said distal end of said inner member extending beyond saiddistal end of said outer sheath; (c) a plurality of elongate blades eachhaving a proximal end interconnected with said outer sheath and a distalend interconnected with said inner member; (d) means for moving saidinner member with respect to said outer sheath so as to retract saiddistal end of said inner member toward said distal end of said outersheath and flex said blades into a radially outwardly bowed arcuateconfiguration; and (e) at least some of said blades defining respectivesharp edges, at least a portion of each said sharp edge extendingalongside said inner member and being oriented more toward said proximalends than toward said distal ends of said outer sheath and said innermember when said blades are in said outwardly bowed arcuateconfiguration, so as to engage plaque associated with an inner wall ofan artery cuttingly as said catheter atherotome is moved within saidartery in a proximal direction, without engaging said interior wall ofsaid artery cuttingly as said catheter atherotome is moved within saidartery in a distal direction and some of said blades being free fromsharp edges and being located opposite said blades defining sharp edges,so as to contact an interior surface of an artery and distend saidartery when said blades are in said radially outwardly bowed arcuateconfiguration.
 19. A catheter atherotome for use in surgical removal ofplaque from the interior wall of an artery, comprising:(a) an elongatetubular outer sheath having respective proximal and distal ends; (b) anelongate tubular inner member disposed within said outer sheath andhaving respective proximal and distal ends, said distal end of saidinner member extending beyond said distal end of said outer sheath; (c)a plurality of elongate knife blades each having a proximal endinterconnected with said outer sheath and a distal end interconnectedwith said inner member; (d) means for moving said inner member withrespect to said outer sheath so as to retract said distal end of saidinner member toward said distal end of said outer sheath and flex saidknife blades into a radially outwardly bowed arcuate configurationdefining a cutting diameter; and (e) said knife blades having sharpenedfront edges and blunt back margins, each of said knife blades includinga middle portion, defining said sharpened front edge, and a pair ofopposite intermediate portions, said intermediate portions beingsufficiently more flexible than said middle portion that said middleportion substantially retains its original shape as said knife bladeflexes into said outwardly bowed configuration and said sharpened frontedges overlapping one another about said outer sheath and being orientedmore toward said proximal ends than toward said distal ends of saidouter sheath and said inner member when said knife blades are at any ofa plurality of predetermined cutting diameters, providing completecircumferential coverage of said artery so as to cut through a stenoticlesion as said catheter atherotome is moved in the proximal direction insaid artery.
 20. The catheter atherotome of claim 19 wherein said innermember defines interior bore means for receiving a guide wire forguiding said catheter atherotome within said artery.
 21. The catheteratherotome of claim 19, said plurality of knife blades defining a basketwhen said distal end of said tubular inner member is retracted towardsaid distal end of said outer sheath, said basket defining an equatorportion and said sharpened front edges of said knife blades beinglocated in said equator portion of said basket and being directedspirally with respect to said outer sheath of said catheter atherotome.22. The catheter atherotome of claim 19 wherein each of said elongateknife blades includes flexible portions thereof which are free ofsharpened edges.
 23. The catheter atherotome of claim 19 wherein saidinner member defines a central longitudinal axis, said intermediateportions being resiliently flexible and twistable, and said middleportions each including a respective one of said sharpened front edges,each sharpened front edge normally being oriented spirally about saidcentral longitudinal axis and defining an angle of incidence, said angleof incidence being shallow enough that said sharpened edge will notcuttingly engage the surface of healthy interior tissue of an artery butgreat enough so that said sharpened edge will cuttingly engageatherosclerotic plaque projecting from the interior surfaces of anartery, said intermediate portions being torsionally elastic enough totwist sufficiently to permit said middle portions of said blades toreach a position in which said edges can engage and pare away saidplaque material from said interior surfaces of said artery.
 24. Thecatheter atherotome of claim 19 wherein said inner member defines acentral longitudinal axis, and including means for preventing at leastone of aid ends of each of said knife blades from rotating with respectto said outer sheath and said inner member about an axis extendinggenerally parallel with said central longitudinal axis, while permittinga terminal portion of each of said knife blades to pivot in a radialplane including said central longitudinal axis, between a position inwhich said terminal portion extends generally parallel with saidlongitudinal axis and a position in which said terminal portion extendsaway from said longitudinal axis at an acute angle and said middleportion of said knife blade is displaced radially away from saidlongitudinally axis.
 25. The catheter atherotome of claim 24 whereinsaid terminal portion of each of said knife blades includes means fordefining a bore, said bore defining an axis about which said terminalportion can pivot relative to said inner member and said outer sheath.26. The catheter atherotome of claim 19 wherein said means for movingsaid inner member includes means defining a scale for indicating theposition of said inner member with respect to said outer sheath and thusproviding an indication of a cutting diameter within said artery and formeasuring said artery following removal of said plaque from said artery.27. The catheter atherotome of claim 19 wherein each of said sharpenedfront edges of said knife blades is located in a cutting position,exposed toward said proximal end of said outer sheath and extendinggenerally circumferentially about said inner member when said distal endof said inner member is retracted toward said distal end of said outersheath and said knife blade members are in said outwardly bowed arcuateconfiguration.
 28. A catheter atherotome for use in surgical removal ofplaque from the interior wall of an artery, comprising:(a) an elongatetubular outer sheath having respective proximal and distal ends; (b) anelongate tubular inner member disposed within said outer sheath andhaving respective proximal and distal ends, said distal end of saidinner member extending beyond said distal end of said outer sheath; (c)a plurality of elongate knife blades each having a proximal endinterconnected with said outer sheath and a distal end interconnectedwith said inner member; (d) means for moving said inner member withrespect to said outer sheath so as to retract said distal end of saidinner member toward said distal end of said outer sheath and flex saidknife blades into a radially outwardly bowed arcuate configurationdefining a cutting diameter; and (e) said knife blades having sharpenedfront edges and blunt back margins, and having respective opposite firstand second ends, said first and second ends thereof being angularlyseparated from each other by a controllably variable angle about saidinner member when said knife blades are in said outwardly bowed arcuateconfiguration and said sharpened front edges overlapping one anotherabout said outer sheath and being oriented more toward said proximalends than toward said distal ends of said outer sheath and said innermember when said knife blades are at any of a plurality of predeterminedcutting diameters, providing complete circumferential coverage of saidartery so as to cut through a stenotic lesion as said catheteratherotome is moved in the proximal direction in said artery.
 29. Acatheter atherotome for use in surgical removal of plaque from theinterior wall of an artery, comprising:(a) an elongate tubular outersheath having respective proximal and distal ends; (b) an elongatetubular inner member disposed within said outer sheath and havingrespective proximal and distal ends, said distal end of said innermember extending beyond said distal end of said outer sheath; (c) aplurality of elongate knife blades each having a proximal endinterconnected with said outer sheath and a distal end interconnectedwith said inner member; (d) means for moving said inner member withrespect to said outer sheath so as to retract said distal end of saidinner member toward said distal end of said outer sheath and flex saidknife blades into a radially outwardly bowed arcuate configurationdefining a cutting diameter; and (e) said knife blades having sharpenedfront edges and blunt back margins, said means for moving said innermember including means for rotating said inner member with respect tosaid outer sheath, so as to alter the inclination of said sharpenedfront edges with respect to said outer sheath and thus with respect to astenotic lesion to be cut by said catheter atherotome and said sharpenedfront edges overlapping one another about said outer sheath and beingoriented more toward said proximal ends than toward said distal ends ofsaid outer sheath and said inner member when said knife blades are atany of a plurality of predetermined cutting diameters, providingcomplete circumferential coverage of said artery so as to cut through astenotic lesion as said catheter atherotome is moved in the proximaldirection in said artery.
 30. A catheter atherotome for use in surgicalremoval of plaque from the interior wall of an artery, comprising:(a) anelongate tubular outer sheath having respective proximal and distalends; (b) an elongate tubular inner member disposed within said outersheath and having respective proximal and distal ends, said distal endof said inner member extending beyond said distal end of said outersheath; (c) a plurality of elongate knife blades each having a proximalend interconnected with said outer sheath and a distal endinterconnected with said inner member; (d) means for moving said innermember with respect to said outer sheath so as to retract said distalend of said inner member toward said distal end of said outer sheath andflex said knife blades into a radially outwardly bowed arcuateconfiguration; and (e) at least some of said knife blades definingrespective knife-like sharpened edges, at least a portion of each saidknife-like sharpened edge extending alongside said inner member andfacing generally more toward said proximal ends than toward said distalends of said outer sheath and said inner member when said knife bladesare in said outwardly bowed arcuate configuration, some of said knifeblades being free from sharpened edges and being located oppositerespective ones of said knife blades defining knife-like sharpenededges, so as to contact an interior surface of an artery and supportsaid knife-like sharpened edges with respect to said interior surface ofsaid artery when said knife blades are in said radially outwardly bowedarcuate configuration.
 31. The catheter atherotome of claim 30, saidplurality of knife blades defining a basket when said distal end of saidinner member is retracted toward said distal end of said outer sheath,said basket defining an equator portion and said respective sharpenededges of said knife blades being located in said equator portion of saidbasket and being directed spirally with respect to said outer sheath ofsaid catheter atherotome.
 32. The catheter atherotome of claim 30wherein each of said elongate knives includes flexible portions thereofwhich are free of sharpened edges.
 33. The catheter atherotome of claim30 wherein each of said knives defining a sharpened edge includes amiddle portion defining said sharpened edge and a pair of oppositeintermediate portions, said intermediate portions being sufficientlymore flexible than said middle portion that said middle portionsubstantially retains its original shape as said knife blade flexes intosaid radially outwardly bowed configuration.
 34. The catheter atherotomeof claim 30 wherein each of said knife members defining a sharpened edgeincludes a pair of opposite intermediate portions and a middle portion,said intermediate portions being resiliently flexible and twistable, andsaid middle portion including said sharpened edge and normally beingoriented spirally about a central longitudinal axis of said inner memberand defining an angle of incidence, said angle of incidence beingshallow enough so that said sharpened edge will not cuttingly engage thesurface of healthy interior tissue of an artery but great enough so thatsaid sharpened edge will cuttingly engage atherosclerotic plaqueprojecting from the interior surface of an artery, said intermediateportions being torsionally elastic enough to twist sufficiently topermit said middle portions of said blades to reach a position in whichsaid edges can engage and pare away said plaque from said interiorsurface of said artery.
 35. The catheter atherotome of claim 30 whereinsaid knife blades have respective opposite first and second ends, saidfirst and second ends thereof being angularly separated from each otherby a controllably variable angle about said inner member when saidknives are in said outwardly bowed arcuate configuration.
 36. Thecatheter atherotome of claim 30 wherein said inner tubular memberdefines a central longitudinal axis, and including means for preventingat least one of said ends of each of said knife blades from rotatingwith respect to said outer sheath and said inner tubular member about anaxis extending generally parallel with said central longitudinal axis,while permitting a terminal portion of each of said knives to pivot in aradial plane including said central longitudinal axis, between aposition in which said terminal portion extends generally parallel withsaid longitudinal axis and a position in which said terminal portionextends away from said longitudinal axis at an acute angle and saidmiddle portion of said knife is displaced radially away from saidlongitudinal axis.
 37. The catheter atherotome of claim 36 wherein saidterminal portion of each of said knife blades includes means fordefining a bore, said bore defining an axis about which said terminalportion can pivot relative to said inner member and said outer sheath.38. The catheter atherotome of claim 30 wherein said means for movingsaid inner member includes means for rotating said inner member withrespect to said outer sheath, so as to alter the inclination of saidsharpened front edges with respect to said outer sheath and thus withrespect to a stenotic lesion to be cut by said catheter atherotome. 39.The catheter atherotome of claim 30 wherein said means for moving saidinner member includes means defining a scale for indicating the positionof said inner member with respect to said outer sheath and thusproviding an indication of a cutting diameter within said artery and formeasuring said artery following removal of said plaque from said artery.40. The catheter atherotome of claim 30 wherein each of said sharpenededges of said knife blades is located in a cutting position, exposedtoward said proximal end of said outer sheath and extending generallycircumferentially about said inner member when said distal end of saidinner member is retracted toward said distal end of said outer sheathand said knife blade members are in said outwardly bowed arcuateconfiguration.
 41. The catheter atherotome of claim 30 wherein at leastone of said knife blades which are free from sharpened edges is locatedso as to distend said artery when said knife blades are in said radiallyoutwardly bowed arcuate configuration.
 42. The catheter atherotome ofclaim 30 wherein said inner member defines lumen means for receiving aguide wire extending through said inner member for guiding said catheteratherotome within said artery.